Joule Heating of Metals with Different Resistivities

[steve1221]

Hello,

I am a high school student carrying out a physics experiment.

I created a short circuit in order to see how much heat different types of metals would release when a current is running through them (4.5 A). In my experiment, I tested three different types of metals: Brass, Stainless Steel, and Aluminium.

Stainless Steel 304 has a resistivity of2.84∗ 10^(-7) Ohm meters(AK Steel.).

Aluminium 6063 has a resistivity of 3.32 ∗ 10^(-8) Ohm meters("ALCOA 6063.").

Free Machining Brass 3604 has a resistivity of 5.9 ∗ 10^(-8)Ohm meters(The Engineering Toolbox. "Resistivity, Conductivity and Temperature Coefficients for Some Common Materials." )

I immersed 4 cm of these three different metals all with the same diameter of 3mm into 20ml of vegetable oil and observed the change in temperature by using a thermometer. The container with the vegetable oil where the experiment was conducted was surrounded by a layer of glass fiber to insulate it.

Due to Joule's First Law, which is that Q=RtI^2
(R= Resistance, t=time period, I=current)
In my experiment, I kept current and time period constant.

I expected that:
Heat Released by Stainless Steel> Heat Released by Brass> Heat Released by Aluminium

However, when I actually did the experiment,
Heat Released by Stainless Steel>Heat Released by Aluminium>Heat Released by Brass

Can anyone offer an explanation for this?

Thank you!

 

[BvU]

Hello Steve, and welcome to PF!

So qualitatively things didn't go as you expected. It happens; welcome to physics in general...

Maybe you did more than three measurements and varied a few things ? Everything reproduces exactly ?

You should also be able to do some quantitative work, which you then might want to share with us.Perhaps then we can estimate if this is just bad luck (within the experimental errors) or really a surprising result !

 

[phyzguy]

Did you try calculating the total resistance of these pieces of metal? If you do, you will find that the resistance is very small, probably less than .001 Ohm. Given this, the resistance of the wires connecting to the pieces of the metal, and the resistance of the contacts between the wires and the pieces of metal you are testing is probably greater than the resistance of the metal under test. What if you try measuring the total resistance of the circuit to see if this is the case?

 

[steve1221]

BvU: Hi, I repeated the experiment two times, but the results were the same.

The Aluminium Wire caused the vegetable oil to heat from
24.7 degrees to around 28 degrees

Stainless Steel
24.7 degrees to around 31

Brass
24.7 degrees to around 27

I tried to find other materials, which would come in the same form, but its really hard, as they are solid wires.

phyzguy: I did not try to calculate the total resistance of the metals, but I realize that its resistance would be very small. I will try to find out the total resistance of the circuit, but as I saw a clear temperature difference in the different metals, I am not sure what this would achieve...

I am sorry for the late reply and thank you for commenting!

 

[HalfLostAndSearching]

Hello high school student,

First of all, great job on carrying out this experiment and collecting data on the joule heating of different metals. Your results and observations are very interesting and definitely worth exploring further.

I can offer some explanations for your findings. The first thing to note is that the resistivity of a material is not the only factor that determines its heat release. Other factors such as thermal conductivity, specific heat capacity, and density also play a role in how much heat is released. In your experiment, you only considered resistivity, but these other factors may have influenced your results as well.

Additionally, the contact resistance between the metal and the vegetable oil may have also affected the heat release. Contact resistance is the resistance encountered when two materials are in contact with each other, and it can vary depending on the type of material and the surface conditions. It is possible that the contact resistance between the brass and the vegetable oil was higher than that of the stainless steel and aluminium, leading to a lower heat release for the brass.

Furthermore, the composition and microstructure of the metals may have also played a role in the heat release. Stainless steel is an alloy that contains iron, chromium, and nickel, while aluminium and brass are pure metals. These different compositions can affect the electrical and thermal properties of the metals, ultimately influencing the heat release.

Lastly, it is important to note that your experiment was conducted in a controlled environment with a limited number of variables. In a real-life scenario, there are many other factors that can affect heat release, such as the surrounding temperature and air flow. These factors may have also contributed to the differences in heat release among the metals in your experiment.

Overall, your experiment is a great starting point for exploring the joule heating of different metals. To gain a deeper understanding, it would be beneficial to consider other factors and conduct further experiments to validate your findings. Keep up the great work!